Electric slag refining process and apparatus

ABSTRACT

To produce an ingot consisting of a metal alloy, substantially the entire ingot is formed in an ingot mold by fusing down remelting electrode material in a liquid slag bath contained in said mold while electric a.c. power is supplied to said slag bath from first a.c. transformer means. The ingot in said mold is subsequently subjected to top end heating in that electric a.c. power is supplied to said liquid slag bath from second a.c. transformer means having a lower nominal power than said first transformer means.

United States Patent [191 Holzgritber et al.

1 ELECTRIC SLAG REFINING PROCESS AND APPARATUS [75] Inventors: Wolfgangl-lolzgruber, Kapfenberg;

Peter Machner, Leoben; Adolf Schneihofer, Kapfenberg; OtmarKleinhagauer, Kapfanberg; Peter Cerwenka, Kapfenberg, all of Austria[73] Assignee: Gebr. Bohler & Co. AG., Vienna,

Austria [22] Filed: June 6, 1972 [21] Appl. No.: 260,122

v [30] Foreign Application Priority Data June 9, 197] Austria 4973 [52]US. Cl. 13/12, 13/34 [51] Int. Cl. "051) 3/60 [58] Field of Search 13/9,12, 9 ES, 13, 13/34 [4 1 Dec. 25, 1973 [56] References Cited UNITEDSTATES PATENTS 3,410,946 11/1968 Dilling et a1. 13/12 X 3,665,080 5/1972Medovar 13/9 ES Primary Examiner-Roy N. Envall, Jr. Attorney-Arthur O.Klein [5 7] ABSTRACT To produce an ingot consisting of a metal alloy,substantially the entire ingot'is formed in an ingot mold by fusing downremelting electrode material in a liquid slag bath contained in saidmold while electric ac. power is supplied to said slag bath from firsta.c. transv former means. The ingot in said mold is subsequentlysubjected to top end heating in that electric ac power is supplied tosaid liquid slag bath from second a.c. transformer means having a lowernominal power than said first transformer means.

3 Claims, 1 Drawing Figure 1 ELECTRIC SLAG REFKNING PROCESS ANDAPPARATUS This invention relates to an electric slag refining processfor making ingots from metal alloys, particularly steel alloys, and anapparatus for carrying out the process.

In the known process, an ingot is produced in that a consumableelectrode which is similar in kind is continuously fused down in a slaglayer, which is heated by electric resistance heating by means ofalternating current which is passed through the layer. As a result, the

electrode immersed into the slag is fused down and the dripping metal iscollected in a water-cooled ingot mold, where the molten metal iscontinuously solidified. The resulting ingot has a main direction ofcrystallization from bottom to top. This results in a particularly goodstructure of the ingot. The ingot grows at a velocity of only a fewmillimeters per minute, and there is always a liquid sump during theremelting operation. That sump has a depth which is about one-half ofthe diameter of the ingot. When the ingot has grown to the desiredheight, the voltage applied to the slag is reduced so that the powersupplied to the slag is lowered to about one-sixth to one-eighth of fullpower. The slag is held at a temperature above the liquidus temperatureof the metal, and metal is melted from the electrode only in the amountrequired to compensate the contraction. This part of the operation isdescribed as top end heating and serves to ensure a solidification ofthe top end of the ingot without formation of a pipe.

Considerable time is required for said top end heating, particularly inthe production of ingots of large diameter. With ingots which are, e.g.,1,000 millimeters in diameter, the top end heating takes 3-4 hours andthis time increases to more than 30 hours with ingots which are about3,000 millimeters in diameter. As a result, the production rate of suchapparatus in the production of ingots having such diameters is reducedby -30 percent or even more, depending on the diameter and'length of theingots which are produced.

It is an object of the invention to avoid said disadvantage. Toaccomplish this object it is proposed according to the invention toproduce an ingot by a remelting operationin which two a.c. transformershaving different rated powers are used and to use the transformer havingthe lower rated power for the top end heating. Hence, the processaccording to the invention requires an apparatus having a secondtransformer. The costs of such a second transformer is relatively lowbecause it requires only a nominal power of 10-20 percent of the nominalpower of the actual remelting transformer. On the other hand, theproduction rate of the plant is increased to such an extent that theexpenditure involved in providing the additional transformer isinsignificant. For instance, during the production of an ingot which is3,000 millimeters in diameter, the top end of said ingot may be heatedby means of the additional transformer and another ingot can be formedup to a height of about 2 meters at the same time by means of the nowfree main transformer.

An electric slag refining apparatus for carrying out the processaccording to the invention thus comprises two a.c. transformers havingdifferent rated powers and comprises apparatus for switching the powersupply from the transformer having a high rated power to the transformerhaving the lower rated power. The means used to change the power dependon the type of the plant and may be of various types. If the smeltingapparatus is designed to remelt a single electrode so as to form asingle ingot, the two transformers and the associated electrode feederare arranged one beside the other, and the water-cooled bottom plate andthe water cooled ingot mold are mounted on a carriage which is movableon wheels between the two electrode feeders. When the ingot has grown tothe desired height, the carriage with the bottom plate and ingot mold ismoved under that electrode feeder which is fed by the transformer havingthe lower rated power. If the plant is designed, however, to producehigher ingots and for this purpose is provided with a so-called liftableingot mold, additional means are required to hold the ingot mold inposition on the carriage during the movement to the electrode feeder fortop end heating. Those means may comprise special supports for the ingotmold of clamping jaws, which .are applied to the lower edge of the ingotmold and operable to clamp the ingot mold on the ingot. If the ingot isproduced from a plurality of electrodes fused down in succession, theelectrode feeders associated with the transformer having the higherrated power and those associated with the transformer having the lowerinput power comprise the known means for a rapid replacement of theconsumed electrode by a new one, e.g., each feeder may comprise twocolumns provided with pivoted electrode-lifting device.

In that case, a preferred embodiment of the apparatus according to theinvention may be used, in which no carriage is used to move the ingotunder the electrode feeder fed by the transformer having the lower ratedpower, but two stations for supporting the bottom plate and ingot areprovided. The electrode feeder which is fed by the transformer havingthe higher power may selectively serve two stations. In this case, theelectrode feeder for top end heating, which feeder is fed by thetransformer having the lower rated power, is either movable on wheelsbetween the two stations so that it can be selectively used at eachstation, or each station is provided with an electrode feeder for topend heating, and each of said feeders can be connected to thetransformer having the lower power.

The economy of the remelting apparatus according to the invention may befurther increased in that the electrode feeder connected to thetransformer having a lower power is used for remelting smaller ingotsduring the time in which said apparatus is not required for top endheating.

Finally, a remelting plant for a simultaneous production of a pluralityof large ingots may be provided with a single electrode feeder for topend heating in a plurality of remelting units. In this case, the largeingots may be made in succession with such timing that a top end heatingof two or more ingots at the same time is not required.

it is apparent that the invention may be used in numerous variationswith economically desirable results.

A preferred embodiment of apparatus according to the invention will nowbe explained by way of example with'reference to the drawing showing theapparatus in a top plan view.

The remelting plant comprises two supports for bottom plates 1 and 2, onwhich ingot molds 3 and 4 are mounted, and also comprises electrodefeeders and transformers T1 and T2. The electrode feederscomprise threecolumns 5, 6, and 7 and electrode arms 8, 9, and 10, which are mountedon said columns to be movable vertically along and pivotally about theaxis of carries an electrode and its support rod. The paths of thepivotal movement of the axes of the electrodes and their support rods 11and 12 and 12 and 13 intersect each other. The ingot molds 3 and 4 arearranged at and below the intersection. The electrode arms and theirclamps are connected by flexible cables to a transformer T1 having ahigh nominal power and to a transformer T2 having a lower nominal power.Electric leads connect also the bottom plates 1 and 2 to thetransformers T1 and T2. The means for changing the energy supplycomprise switches 14, 15, 16, and 17.

The remelting apparatus shown on the drawing is operated as follows.Using the electrode arms 8 and 9 remelting electrodes are first fuseddown in the ingot mold 3. In this operation, the ingot mold 3 may beraised in known manner as the ingot grows. The moldlifting means, notshown, may be guided along the column 5. At thebeginning of theremelting operation, it must be ensured that the last electrode to befused down in producing the ingot is to be fed with the arm 8. For thisreson, the first electrode to be fused down is carried by the arm 8 ifthe ingot is to be formed from an even number of remelting electrodes,and by the arm 9 when the ingot is to be formed from an odd number ofremelting electrodes. During the remelting operation using the electrodearms 8 and 9, the switch 14 constantly connects the transformer T1 tothe bottom plate 1 whereas the switch 15 is operated to connect thetransformer to that electrode arm 8 or 9 and to that electrode clampwhich is in remelting position over the ingot mold at any time. Theswitches 16 and 17 are in their intermediate position. When theelectrode arm 8 carrying the last electrode to be used in forming theblock has been swung to its remelting position, the first electrode forthe ingot to be formed in the ingot mold 4 on the bottom plate 2 is hunginto the arm 9 or 10. The arm is again selected so that the lastremelting electrode to be used in forming the ingot is fed with the arm10. Because the top end heating is carried out with a lower power andwith a lower fusing-down rate, only part of the last remelting electrodeis generally required same time, the switches 16 and 17 are moved to theupper position shown on the drawing so that the power required for thetop end heating of the first ingot is supplied from the transformer T2having a lower nominal power. When the top end heating of the firstingot has been terminated, the same is removed from the plant and thebottom plate 1 and the ingot mold3 are preparedfor the remelting to formthe third ingot. The remelting to form the second ingot is effected ashas been described for the first ingot. It will be understood that thevarious switches must be moved to the positions required for thispurpose.

Although the invention is illustrated and described with reference to aplurality of preferred embodiments thereof, it is to be expresslyunderstood that it is in no way limited to the disclosure of such aplurality of preferred embodiments, but is capable of numerous m odi- 1.An electric slag refining process of producing ingots consisting of ametal alloy, which comprises building substantially an entire ingot inaningot mold by fusing down remelting electrode material in a liquidslag bath contained in said mold while supplying electric a.c. power tosaid slag bath from first a.c. transformer means, and

subsequently subjecting said ingot in said mold to top end heating bysupplying electric ac. power to said liquid slag bath from second a.c.transformer means having a lower nominal power than said firsttransformer means.

2. A process as set forth in claim 1, in which remelting electrodematerial consisting of an alloy steel is fused down.

3. Electric slag refining apparatus for producing ingots consisting ofmetal alloys, which comprises at least one ingot mold adapted to containa liquid slag bath,

holding means for holding remelting electrode material adapted to befused down in said liquid slag bath to form in said mold an ingot undersaid liquid slag bath,

first a.c. transformer means,

second a.c. transformer means having a lower nominal power than saidfirst transformer means, and switch means adapted to alternativelyconnect said first and second transformer means to supply electric ac.power to said slag bath.

1. An electric slag refining process of producing ingots consisting of ametal alloy, which comprises building substantially an entire ingot inan ingot mold by fusing down remeLting electrode material in a liquidslag bath contained in said mold while supplying electric a.c. power tosaid slag bath from first a.c. transformer means, and subsequentlysubjecting said ingot in said mold to top end heating by supplyingelectric a.c. power to said liquid slag bath from second a.c.transformer means having a lower nominal power than said firsttransformer means.
 2. A process as set forth in claim 1, in whichremelting electrode material consisting of an alloy steel is fused down.3. Electric slag refining apparatus for producing ingots consisting ofmetal alloys, which comprises at least one ingot mold adapted to containa liquid slag bath, holding means for holding remelting electrodematerial adapted to be fused down in said liquid slag bath to form insaid mold an ingot under said liquid slag bath, first a.c. transformermeans, second a.c. transformer means having a lower nominal power thansaid first transformer means, and switch means adapted to alternativelyconnect said first and second transformer means to supply electric a.c.power to said slag bath.